The present invention relates to improved method for producing a golf club head, and more particularly relates to improvement in production of a golf club head by heat pressing a compound in a mould.
Among various conventional methods for production of a golf club head, there are two types of molding processes, which are considered as typical ones. One is the injection molding by which viscous material is injected under high pressure into the mold cavity, and remains in the mold under high pressure until it cools, and is then ejected. This molding method, however, has a drawback in that golf club heads of larger bulk render them heavier than desired. To solve this problem, it has been proposed to use a pair of core halves bonded together to form a cavity therein. Such core halves, however, must be strong enough to endure high pressure at molding, and must attain a correct positioning in the mold. For this, it requires more labor and higher cost.
Further, the conventional injection molding has another drawback in that it is difficult to obtain golf club heads of uniform weight. Among the golf club heads so produced, the weights differ one from the other. The reason is that: the viscous material injected into the mold can be set in a predetermined volume; however, the specific gravity of the material differ each time it is injected, and the resultant weights of the products differ.
The other of the conventional molding processes for production of a golf club head is as follows. A crude core is first prepared by proper preparatory shaping and a crude shell in the form of fiber reinforced plastic is attached to the outer face of the crude core by, for example, manual coating. Thereafter the combined crude body is placed in a mould for heat pressing.
In this case, the amount of the fiber reinforced plastic to be supplied into the mould cavity for production of each golf club head is controlled by weight measurement before individual supply. However, supply of constant weight does not always assure supply of constant bulk of the fiber reinforced plastic because of unavoidable fluctuation in specific gravity of the material containing reinforcing fibers. Thus, the bulk of the fiber reinforced plastic supplied into the mould cavity tends to deviate from the standard which is fixed by the capacity of the mould cavity.
When the resultant bulk is smaller than the standard, i.e. the specific gravity is larger than the standard, the heat pressing is liable to develop lots of surface and inner voids on and in the product which seriously lower the commercial value and mechanical strength of the product. In order to obviate this trouble, it is usual to supply an excessive amount of fiber reinforced plastic into the mould cavity so that the resultant bulk should meet the capacity of the mould cavity even when the specific gravity of the material is larger than the standard. Such excessive supply of fiber reinforced plastic may well avoid the void trouble but it causes another trouble in production. When the specific gravity of the material is on the standard or less, the excessive supply in weight naturally results in a bulk of the supplied fiber reinforced plastic larger than the capacity of the mould cavity which is fixed. As a consequence, the extra bulk of the supplied fiber reinforced plastic seeks asylum in the mould at heat pressing and is forced to permeate into interstices between mating faces of mould halves. This behaviour of the fiber reinforced plastic at heat pressing develops significantly projecting dregs or flash on the surface of the product after heat pressing. These dregs have to be removed for commercial reasons. Removal of such dregs requires additional work, mars the surface quality of the product, and connects to waste of the material. In addition, reinforcing fibers in the shell are more or less broked during the removal, thereby lowering the strength of the golf club head.
In addition to the foregoing, this process has difficulty in correct positioning of the crude core since the crude core must keep a position in the mould cavity to leave the predetermined gap during filling of the crude shell material. Several spacers may be arranged around the crude core in the mould cavity. In this case, however, ends of the spacers appear on the surface of the product and mar the surface quality of the product. Alternatively, one or more supporting arms may be inserted into the mould cavity. In this case, however, inlet of the crude shell material formed in the wall of the mould cavity is directed towards the surface of the crude core in the mould cavity. As a consequence, pressure at filling of the crude shell material directly acts on the crude core supported by the supporting arms and the crude core is liable to loose its initial set position during filling of the crude shell material. Such unexpected displacement of the crude core often poses ill influence on the strength of the shell in the product and further causes incorrect shaping of the product.